Re: Synchronizing slots from primary to standby

Hi,

On Tue, Jan 16, 2024 at 05:27:05PM +0530, shveta malik wrote:
> PFA v62. Details:

Thanks! 

> v62-003:
> It is a new patch which attempts to implement slot-sync worker as a
> special process which is neither a bgworker nor an Auxiliary process.
> Here we get the benefit of converting enable_syncslot to a PGC_SIGHUP
> Guc rather than PGC_POSTMASTER. We launch the slot-sync worker only if
> it is hot-standby and 'enable_syncslot' is ON.

The implementation looks reasonable to me (from what I can see some parts is
copy/paste from an already existing "special" process and some parts are
"sync slot" specific) which makes fully sense.

A few remarks:

1 ===
+                * Was it the slot sycn worker?

Typo: sycn

2 ===
+                * ones), and no walwriter, autovac launcher or bgwriter or slot sync

Instead? "* ones), and no walwriter, autovac launcher, bgwriter or slot sync"

3 ===
+ * restarting slot slyc worker. If stopSignaled is set, the worker will

Typo: slyc

4 ===
+/* Flag to tell if we are in an slot sync worker process */

s/an/a/ ?

5 === (coming from v62-0002)
+       Assert(tuplestore_tuple_count(res->tuplestore) == 1);

Is it even possible for the related query to not return only one row? (I think the 
"count" ensures it).

6 ===
        if (conninfo_changed ||
                primary_slotname_changed ||
+               old_enable_syncslot != enable_syncslot ||
                (old_hot_standby_feedback != hot_standby_feedback))
        {
                ereport(LOG,
                                errmsg("slot sync worker will restart because of"
                                           " a parameter change"));

I don't think "slot sync worker will restart" is true if one change enable_syncslot
from on to off.

IMHO, v62-003 is in good shape and could be merged in v62-002 (that would ease
the review). But let's wait to see if others think differently.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com